Recently, navigation systems, represented by car navigation systems, have been propagated. Car navigation systems perform display of a current position or route guidance to a destination when an automobile travels. The display of a current position or the route guidance to a destination is normally performed on a map displayed on a screen of a navigation terminal. Furthermore, the route guidance may be performed through sound.
As an example of the navigation system, a navigation terminal for a bicycle or walk has also been known in recent years. The navigation terminal for a bicycle or walk may perform route guidance by giving priority to a road with a gentle slope with reference to altitude data in addition to map data. Here, the altitude data, for example, may be acquired from a plurality of images, which have been photographed from the upper air by an airplane, an artificial satellite and the like, through a stereo image process, or may also be acquired using a method of measuring the position and altitude of each point by irradiating laser from an airplane or a satellite using a laser profiler, as disclosed in Patent Literature 1.